Manufacture of perchloric acid



Jmls, 1946. J; C, PERNERT 2,392,861

MANUFAGTURE OF PERCHLQRIC ACID Filed May 18, 1945 4 sheefs-sheet 1 FINISHED CONC-PURE lHC|4 Nac|04 U WASTE ATTORNEY Jan. 15,- 946 v J. c. PERNERT MANUFACTURE F-PERCHLORIG ACID 4 sheets-sheet s Filed May 18, 1945 -INVENTOR JOHN C. PER'NERT, BY

"ATTORNEY Jan. 15, 146. J. c. PERNERT.

MANUFAGTURE OF PERCHLORIC ACID 4 sheets-sheet 4 Filed May 18, 1943 INVENTOR JOHN C. PERNERT,

FIG- 4..-

ATTORNEY y anni@ Jan. is, iste l. AT S AIT i AcTUm: oF mnemonic acm `lohn C. Pernert, Niagara. Falls, N. Y.,

y Oldbury Electro-Chemical Co.,

assigner to Niagara Falls,

N. Y., a corporation of New York Application May 1s, 1943, serial No. 487,498

(ci. zs-isz) 6 Claims.

namely, sodium perchlorate is reacted with hydrochloric acid to yield perchloric acid and sodium chloride. The perchloric acid is .f then treated to concentrate and purify it, so that such acid is the desired end product of this invention.

In the practice of a commercial scale process of making perchloric acid, the initial reaction product acid is yielded along with certain contaminating impurities which comprise admixtures such as other reaction products, some unreacted reactants, and which also may or may not include other undesirable substances. Therefore, one object of this invention is to remove such contaminatingimpurities expeditiously, andfif possible to reclaim any impurities which may be usable as additional starting reactant materials. Another object of this invention is to bring about the yielding of the perchloric acid in purified and concentrated condition, namely of the order of from 70% to '72% or slightly higher concentration. A further object is to control the degree of concentration of the acid yielded. Another object is to produce the acid cheaply, dependably and continuously, while requiring a minimum of attention. Y

To that end, this invention may be better understood by dividing the perchloric acid making plant into different stations. Of these, the first may be called the reaction station wherein the- .raw starting materials are reacted; a first filter station; a concentrated HCl removing station; a perchloric acid concentrating station; a distilling station; and a second filter station.

In general, the functions of these stations are as follows: In the reaction station, called hereinafter Reactor, for short, the raw reactant starting materials are brought into contact with eacli other under conditions where reaction takes placeand reaction products yielded. These products include NaCl and a complex dilute liquor comprising H20 and the following ions H+, Na t, Cir, 0104-, and possibly other constituents. The reaction products are then passed to a first filter station whose principal function is to filter out NaCl from the complex liquor. The filtrant is fed to the H0104 distilling station, called hereliquor is then supplied to the' concentrated HC1 removing station, which will be referred to here-- inafter for short, as the Remover. One purpose of the Remover is to remove and reclaim from thel complex liquor ,fed thereto, HCl distillate in solution form whose HC1 concentration is controllable at will. The residual complex liquor next passesV to the perchloric acid concentration station, called for short hereinafter the Concentrator, from which is derived essentially concentrated but impure H0104. Such impure H0104 inafter, the Still, from which is derived concentrated pure HC104 as the desired end product. and another product comprising a complex mixture including NaCl04 and impure H0104. This mixture is passed to a second filter station whose l function is to separate the NaCl04 from the H0104. The separated-out NaClO4 and the concentrated HC1 are or can be recycled to the Reactor to be used to supplement the raw starting reactant materials in the Reactor.

Features of advantage iiow not only from the specific construction and arrangement of these stations per se, but also from the manne-'r iny which they are connected and interconnected, as well as from their conjoint action. A feature i of importance is that at least some of these stations make use of the barometric leg principle and operate under sub-atmospheric pressure while associated therewith is a system of a boiler followed by stagewise condensation, all of which ,contributes to the attainment of new and novel results. Another feature of importance and advantage is the boiler arrangement of both the Concentrator and the Still wherein the vaporized constituents' of the treated material pass upwardly while the left-behind products remove themselves from the boiler by gravity.

Still another feature of advantage is derived from the Still that has thev property `of being self-feeding at a rate that is automatically controlled so that the quantity of material fed thereto is always correct. A further feature is the useof a vertical, steam-jacketed glass tube boiler, A still further feature is embodied in means for maintaining the position of solutions to be treated in such a boiler, at a :proper working level therein by the use of a barometric'leg. Again, anadditional feature resides inthe barometric leg means whereby solid non-volatile residue is continuously and automatically removed in the Still. Another resides in the use of the hot condenserl principle to be later .described herein. And even further advantages will be made clear chloric acid. 4

For a more particular understanding of this invention, a preferred embodiment of the invention has been illustrated in the accompanying drawings, in which Figure 1 shows diagrammatically the arrangement of the various stations depended upon for conjoint action. Fig. 2 is a diagrammatic showing ofthe Remover,'the Concentrator and the Still stations Iwithout any attempt at showing them complete, but lenough-to gi've an idea of their general construction and function. Fig. 3 shows diagrammatically what Fig. 2 shows, but greater detail is made use oi.

Fig. 4 shows a detail of the liquid-level as it functions in the boiler or vaporizing zones, the view being a' partial perspective one, with parts broken away and also shows a detail of the Kjeldahl bulb as being illustrative of what may be used to trap spray splashing forwardly from the solution in the boiler zone of the Still so that such solids are returned to the boiler zone.

Referring to Fig. 1, the numeral II indicates generally the starting materials comprising essen- -tially the reactants NaClO4 andI HC1 in solution thatfare fed to a stirred or agitated reaction vessel or Reactor 12 wherein reaction takes place to yield HClO4 and NaCl. Reaction products are passed through pipe I3 to a nlter station I4, called herein the first filter station, whose function is to discharge by one path I5. solid phase material present in the reaction magma, especially such as NaCl, while filtrate which comprises raw starting liquor IS- passes forwardly from the illter I4 `to the HC1 Remover I1. The operation the stations thereof. lPassing now' to Fig. 2, which although still diagrammatic, shows some of the fundamental features of operation of the Remover, the Concentrator, and the Still stations respectively. Considering the Remover I'I, it is made up of a boiler or vaporizing zone 32 appropriately heated to a temperature above which HCl vaporizes, that is connected witha discharge pipe 34 and a vapor conducting pipe 30 from its upper section that conducts vapor to a condenser 33 having a discharge pipe I8 from which a concentrated solution of HC1 is obtained. The raw dilute starting liquor I6 from the lter station I4 is supplied to the Remover Il through pipe 3i connected to the Remover at a point adiacent the upper region of the boiler zone, and discharged impure HCloi-bearing complex liquor Y .from theV boiler zone passes out of the pipe 34 to be accumulated in a container 35, whence it is drawn for further treatment. preferably operates at atmopheric pressure, and distillate solution therefrom is controlled to comprise HC1, having .a specific gravity of 1.178, although this concentration can be changed by the rate of feed to the Remover.

- Turning attention now to the Concentrator 20, it comprises essentially a ilowpath of tubing in which suction can be maintained and through which is impelled, complex HClOt-bearing liquor from which a quantity of HC1 and of Hzohas been removed in the Removervil. During transit of the complex liquor through the owpath, H0104 is concentrated but not substantially othof the Removeris based upon the property of the solutions so treated to evolve HC1 gas along with very little H2O, whereby the proportion of HCl to H2O in the distillate solution can be controlled at will by the rate at which the liquor is fed to the Remover, the faster the rate the more concentrated the HC1 in the solution, and vice versa. Therefore, the function of the Remover is to yield a distillate solution having therein such a controlled concentration of HC1 I8 that it can be recycled to be used as a partial or supplemental constituent of the starting materials Il, that is, about 3,5% HCl by weight and H20 by weight, which is equivalent to what is known as commercial hydrochloric acid. The Remover I1 also yields bv another pathway, possibly valved at V' (Fig. 2) a complex dilute liquorl I9 that is treated in the HClOt Concentrator 20. 'Ihis station or instrument discharges waste material 2I by one pathway, while passing on through another pathway a somewhat concentrated but still complex liquor 22 which contains concentrated but impure H0104, which complex' liquor is next treated in the Still 23. From the Still 23 there is discharged waste 24 by one pathway, and through another pathway is passed concentrated purified' HClO4 25. rIlhrough another pathway, if desired. is passed on a liquor or liquid suspension 25' of concentrated H0104 and NaClO4. This suspension is supplied to second filter station 26 which is adapted to yield as filtrate, HClO4 21, and to yield as the other illter product or vfiltrant 28, NaClO4 which is or can .be recycled to be used as a partial or supplemental constituent of the starting materials II.

Thus Fig. 1 discloses `what may be termed av general flowsheet or now-chart of one embodiment of this invention showing the sequence of erwise purified. This Concentrator station is characterized by a vaporizing or boiler zone 39 maintained at a temperature'whereat at least water is vaporlzed in that. zone under the conditions existing therein. Liquor I8 to be treated in the Concentrator is automatically sucked there- 40 into through the pipe 36 from the liquor container 35. Feed pipe 36 joins the Concentrator ZI) at a point 31 above the boiler 39. Associated with the boiler zone 39 is a barometric leg 40 liquid-sealed in s. pool of liquid 4I which is concentrated H0104 held in a-basin 42. Associated with the upper section of the boiler 39 is a tube 45 forming a vapor conveying passage leading to a Hot Condenser zone 44 maintained at a temperature above that at which water boils under the conditions existingtherein. Associated with this Hot Condenser 44 is a barometric leg 48 liquidsealed in a pool of liquid 41 which is impure concentrated H010; held in a basin 48.

Vapors pass from the Hot Condenser 444 upwardly and forwardly through a tube 5I to a Cold Condenser 50 preferably of the spray type. The Cold Condenser has associated with it a barometric leg 52 liquid-sealedin a pool of waste liquid 53 held in a basin 54, from which basin, liquid 53 passes to waste through pipe 2 I. 43 indicates a tube or pipe leading to a vacuum producer adapted also to suck vaporous material of the Concentrator 20 upwardly and forwardly through the boiler zone 33 and the subsequent Hot Condenser zone 44 and Cold Condenser zone 50. Since there is a sub-atmospheric pressure thus effected in the iiowpath tubing of the Concentrator 20, the barometric legs '40, 46 and 52 must be of such a length that at least their liquid column contents respectively are not sucked out thereof'by reason of the suction exerted by the vacuum producer. The boiler zone 33 is so related to its barometric leg 40 that the range of normal iluctuations of the liquid-level of the liquid column therein lie well within the boiler zone The Remover 39. And similarly, the Hot Condenserv zone Il is however, from' mos't 'of its HC1 content. Therefore, the'boiler zone 39 is heated at'leastso that the'volatizable impurities (such as H2O) oi the back to the boiler zone 39. And this require-` t ment is also essentialwith respect to the Cold Condenser zone i) for liquid therefrom must not iiow back through 5I 4to the Hot Condenser. Concentrated HClO4 4| is discharged from the barometric leg di) while still hot, or at least warm, so -that under operating conditions there is little or no separation of NaCl04 from this liquor. This liquor, together with the impure H0104 4'! inbasin da are both supplied through conduit 22 or other means, to be ltreated in the Still 23, or in some instances, the basins d2 and 59 one and the same.

Turning now toA the Still station 23, its apparatus closely resembles the apparatus of the Concentrator 2li), as can be seen from Fig. 2, but the internal conditions are somewhat diierent, especially as regards temperature, for whereas in the Concentrator, H0104 is concentrated substantially irrespective of its impurities, in the Still the'concentrated acid is to be relieved of its non-volatile impurities and at'the same time the degree of concentration ofthe obtained pure acid is accurately controlled. Therefore, 56 indicates the vaporizing or boiler zone of the Still wherein is maintained a temperature above that at which H0104 lvaporizes under conditions of pressure existing in that zone. Associated therewith is a barometric leg 5l liquid-sealed in a. pool of concentrated liquor 58 which is heldin concentratedliquor basin 59. In basin 59, there is an accumulating of non-volatiles most of which crystallize out as NaCl04, so liquor 58 becomes substantially satura-ted with this salt, whereupon it can be iiltered therefrom in iilter 28 by being passed thereto through pipe 25'. This liquor also includes the complexliquor 22 from the Concentrator 2Q, which is the starting material to be treated by the Still, for it is sucked automatically up through the barometric leg 51 as itis required lby the boiler 56. vapors from the boiler 56 are sucked through pipe @I to a Hot'Condenser 60 which has associated therewith a barometric leg 52 that is liquid-sealed in a pool of liquid t3 held in basin dit. Liquid t3 comprises the desired concentrated purified perchloric acid. Vapors passing from the Hot Condenser t@ are conveyed through pipe td to the Cold Condenser S5 which also has a barometric leg el that is liquid-sealed in a pool of liquid to in basin ed. 'it indicates a vacuum producer, such as a hydraulic vacuum pump, which produces the vacuum and suction in the owpath piping. The same precautions of liquid level requirements in the respective barometric legs of the Concentrator 2U appliesY equally to the corresponding legs of the Still. 'I'he temperature maintained in the Hot Condenser 6B is such lthat H0104, along with suiiicient water to give the required concentration of H0104 solution, is selectively condensed from the HClO4- bearing gases or vapors which vapors that escape condensation here pass on to be condensed later in other condensers such as the Cold Condenser 65.

Comparing the Concentrator 20 with the Still l 23, the following is to be observed: to the Concentrator is automatically fed, as fast as produced by the Remover il, a starting material i9 vof a complex dilute liquor which has been freed may be H0104 -will be vaporized but with a minimized quantity of HC104 being also vaporized. Thus H0104 so treated, descends with any solids suspended therein, downwardly through the column of liquid in the barometric leg t0. The 'vaporized constituents pass to the Hot Condenser M wherein they are only partially cooled to a temperature whereat -(as correlated to the subatmospheric pressure existing therein) any perchloric acid which may have reached that Con,

denser is condensed, while the other volatilizable impurities pass forward to be condensed in the Cold Condenser-50 and passed to waste. However, when the Still is considered the vaporizing or boiler zone 56 is maintained at a temperature correlatedwith the pressure eiiective therein, so

that at least perchloric acid is vaporized therein ,along with all vaporizable impurities that may .be mixed therewith. yThe non-volatile materials (ranging possibly from 1% to 9% of the solution), are left behind and descend in the liquid column in the barometric leg 5l.l The vapors pass to the Hot Condenser which is cooled enough to condense the HC104 while letting the other vaporized constituents go forward to be condensed in the Cold Condenser and passto I waste. From the Hot Condenser 60, condensed andpurified H0104 descends in the liquid column in the barometric leg $2 where thismaterial is coliectedin basin 6d as the end product HC104.

Another diii'erence between the Concentrator and the Still is that the operator controls (even though possibly indirectly), the rate of feed in the pipe 35 passing to the Concentrator, whereas the Still automatically controls its own rate of feed. -It also automaticallyA and continuously discharges non-distillable residue. The strength of the H0104 .recovered from the Still is controlled by correlating the temperature and pressure within therein to yield the desired strength.y

The Concentrator has proven successful when made of 3inch flanged glass whereas in the Still the tubing was of vtwo-inch blown glass. How this all' is accomplished will be described later in detail. The Condenser and the Still both preferably operate under' vacuum. q

From this description of the operation of the process, it can be surmised that the raw dilute complex starting liquor iusupplied to the Concentrator 20 should have as little as possible of sodium salts. For that reason, the original re action in the reaction vessel i2 is carried out.

with a view to minimizing the production of NaCl in any other than in solid phase, so that a minimum vthereof is left in solution. Nevertheless, NaCl is unavoidably soluble to some extent.

to the Process.

'Typical analyses of the liquors at the diierent stages are:

Raw starting liquor i6 HCl-109 g. p. l do 8.1 Non-volatile79.5 g. p. l --do 5.9

Water (by dierence) 730 g. p. l-.. do---- 54.0

Liquor 34 discharged from remove;

Specific gravity.. 1.395 HClO4550 g. p. l -per cent-, 39.4 HCl-l2 g. p, l -do...-- .86 Non-volatile-lOl g. nl .do... 7.24

' H2O (by difference) 732 g. p. l '....--do 52.5

Liquor 4.1 discharged from concentrator Specific gravity 1.58

11010-800 g. p. l ..-per cent-- 57.0

HC1O4-0.6 g. p. l --do 0.04

Non-volatile (NaClO4) 166 g. p. l do 10.5

H2O (bydiiference) 514 g. p. l do 32.46

Finished acid 63 ,from still Specific gravity 1.678

HClO4- -per cent.. 71.0

HC1 less than 0.1 P. P. M.

Non-volatile less than 5 P. P. M.

Iron less than 1 P. P. M.

Thus, comparing the liquor II and the acid 83 of these last two tables the non-volatile impurities have been reduced from 139,000 P. P. M. in the liquor to less than 5 in the finished acid.

It should be understoodthat Fig. 2 and the description thereof does not contain all of the disclosure needed to practice this invention. This ngure and its description has been adopted to help the reader to a better understanding of the invention by leading him along step by step. or a little at a time. until the entire invention is grasped. But at least by now, the reader will -understand the general construction and-.pur-

pose of the respective stations. and especially those of the Concentrator and of the'Still. y

yWith this preparatory information and ground work, reference is now made to Fig. -3 which shows,

ywhile yet diagrammatically, allo'f thelfunilfuimen-` tal principles cfa full commercial scale operating plant for the practice of this invention? This figure follows Fig. 2' closely butfisjexpanded 'as to detalls. In it other details are shown :or each `of the Concentrator and Still stations together with an indication of operative requirements which will now be described.

The general plan of Fig. 3 follows that of Pig.

A 2. in that the Remover i1, the Concentrator 20 and the Still 23, are indicated thereon. Referring tothe Remover station I1, it is constructed of an inverted U-shaped tube having one leg with an intake 8i preferably valved as at V and an other leg with an outlet I8. The two legs are connected by a curved section 30. The outlet leg is equipped with a cooling or condensing zone 88 provided by a cold water jacket encircling the tubing and having a water inlet 1I and a water outlet 12. The intake leg is equipped with a boiler ing and havinga steam inlet I8 and a steam out- 1e: 1s. Associated `with the belier :s is a om" metric leg 40 in which is maintalneda column of liquid 80 rising from the liquid 4l in basin l2. The length of the barometric leg 40, and its liquid column 8o is such that underthe condition obtaining in the tubing. the liquid level Il` of the liquid column is maintained within the boiler zone 88. The fiowpath continues forwardly from the boiler I8 by means of the section 88 of the tubins and curved section I8 to a Hot Condenser Zone indicated generally by' the" numeral M. In the preferred form, this Hot Condenser zone is formed by la further section 82 of the` tubing which has a hot water Jacket 83 encircling the section 82,

' provided with a hotwater inlet 85 and a water outlet 84. The tubing then has a connecting section 88 that connects with the Hot Condenserv barometricleg 48 which contains a column of liquid 81 that due to the suction within the tubing extends upwardly from the pool l1 in basin 48 but never high enough to back ow in section 88. It normally rises to a level about as shown at 88. A forward extension 88 of the barometric leg I8 is provided with another hot water jacket 80 encircling the section 88, provided with a hot water inlet 82 and a water outlet 8i.

5I represents a further section of the tubing iowpath which connects with an intermediate Condenser zone 83 having associated therewith a barometric leg 84 in which is maintained a column of liquid 95 extending from a pool 8B in basin 91. The column rises to a level 88 about as shown,

` but never high enough to back iiow in section li.

The Intermediate Condenser zone 88 comprises a warm'water kjacket encircling the tubing and provided with a warm water inlet I|i0 and a water voutlet icl.

zone 83 is a'further tubing section 5I' that oon- From the exit end of the iacketed.

nects with the Cold Condenser 58 and its barometric leg 52 having maintained therein a column of liquid |02 extending from the pool 53 in basin to a liquid level i08, about as shown, but never high enough to back flow in section 5I'. |04 indicates a cold water spray means, while attached to the piping section I8 leading to a or vaporizing zone 82 provided by a steam jacket encircling the tubing and having a steam inlet 13 and an outlet 1l. The intake leg hasa terminal 34 which is provided with an 8 trap arrangement 'I5 whose high point 15a rises to an elevation such that a pool of liquid 18 is retained in the tubing within the boiler zone 32 so that the liquid level II of the liquid pool I8 is maintained substantially well within the boiler zone I2. about as shown. Liquid passing out through the S-trap 18 is caught in the container Il. 1lb indicates a vent section for the trap to prevent siphonlng.

The Concentrator 2o is constructed to have an intake tube or pipe 88 feeding feed-liquor I8 to a now-path formed of tubing characterized by having a vertical vaporizing or boiler zone 88 provided with a steam Jacket' encircling the tubvacuum producer or pump |05 is a pressure. or

vacuum, regulator I88 and a pressure indicator- Above the boiler zone B8, is a` solids trap such as a K Jeldahl head or bulb I Il. The ilowpath passes on through section 8i to a Hot Condenser zone indicated generally by the numeral and comprises a tubing section I I8 that has encircling it, a hot water jacket III provided 'with' a hot water inlet I I 8 and akwater outlet I l1. The ilowpath then passes through a section II8 which connects with the Hot Condenser barometric leg 82 in which is maintained a column of liquid |28 extended from the pool 83 in 'basin 84 upwardly to have a liquid level I2I atl a level about as shown. Associated with the barometrlc leg 8 2 is another Hot /Condenser comprising tubing section |22 with a jacket having a hot water inlet |219 and a hot water outlet |23. From the exit end of this tubing section |22 is ay connecting pipe 85 that :loins a further barometric leg |25 which may be called the -Intermediate Condenser leg. In it is maintained a column extending from a pool |21 in basin |28, and rising to a liquid level |28 at an elevation about as shown. Associated with this leg |25, is an Intermediate Condenser jacket |30 encircling the tubing and having a warm water inlet 3| and a water outlet |32. |33 indicates a section of the tubing that passes to a Cold' Condenser zone, indicated generally by the numeral 65. This zone is preferably made into two parts or of two units. The rst part comprises a cold Waterjacket |34 encircling a section |35 of the tubing, provided with a cold water inlet |36 anda water outlet |37. The ilowpath progresses forwardly through the connecting tube 65' to the Cold Condenser barometric leg 61 in which is maintained a column of liquid |38, extending from the pool 68 of basin 69 and rising, under the conditions within the tubing, to a liquid level |39, about as shown. Associated with this leg is another Cold Condenser zone or cold jacket |40 having a cold water inlet |4| and a water outlet |42.l The ilowpath then progresses through a section 10 connected with a vacuum producer or pump |33,

and with this section 18 is connected a pressure regulator |33 and a pressure indicator |45.

This gure is drawn substantially to scale, at

least to the extent of showing the relative heights or lengths of the barometric legs, indicated by of liquid |26 an acid strength or proportion of about 35% and water proportion of about 65%, with a typical specific gravity of 1.178. The strength or concentration of the thus obtained acid can be controlled in general, to give a solution say, 20% to saturated, by careful control of the rate of feed of the raw starting liquor to the Remover. Liquorfrom-the pool 16 with its nonvolatilized constituents passes automatically over the high point a of the S-trap 15 to be collected in the container 35. The S-trap I5 has the function of maintaining the liquid level of the pool in the boiler zone 3 2 high enough therein to get efcient vaporizing eiects on the the scale in feet indicated at the left hand side of the ligure. Basins`32 and 58, with their respective pools 3| and 58 can be one and the same, or liquor from one can be conducted to the other, preferably from basin 52 to concentrated liquor basin 59, as indicated bythe line 22. Similarly, if desired the contents or pools of basins 48, 9T and |28 can also be conducted preferably to basin 58. Or again, the contentsy of basins 91 and |28 may be recycled to the Reactor I2 (Fig. 1). The liquor in basins 54 and 69 pass to waste, while the liquor in basin 58 comprises end-product concentrated pure H0104.

exemplified in Fig. 3 is as follows: Theraw starting liquor l5, which comprises the ltrate from the Filter |4 is supplied at a rate controlled, for instance by any control means such as valve V, through inlet 3| to the Remover at an elevation above the top of the boiler zone 32 whence at least some of the liquor falls into the pool 'i6 maintained in the boiler zone 32 by means of the S-trap 15 and its high point 15a. In the boiler zone 32, the liquor has its temperature raised by the steam in the encircling jacket of the boiler zone 32, to a point above the vaporization point of HCl under the conditions of pressure existing in that zone, which are preferably normal atmospheric pressure, or substantially so. At such temperatures, HC1 gas is vaporized from the solutions of the pool 'i5 along with some water. The rate of feed to the Remover controls the proportion of water and of HCl that are vaporized. Thus, the concentration of HC1 in the water vapor can be controlled at will, namely', by the rate of feed to the Remover. The HCl and H2O gases pass over the curved section 36 of the Remover and then through the Condenser zone 33 whereupon on encountering the temperature therein the mixed vapors arevcooled by the cooling water of the Jacket 33, the mixed HCl and H2O gases are condensed as a puriiied distillate solution having pool by the steam in the encircling jacketlof the boiler zone. The liquor in the container 35 is a complex liquor and includes as constituents, H0104, H2O, some unreacted reactants such as NaClO4 and possibly other sodium salts, and other impurities such as compounds of iron.

The operation of the Concentrator apparatus exemplified by Fig.' 3 is as follows: Complex liquor I9 from the container 35 from which a quantity of HC1 and of H2O has been removed, is sucked through inlet pipe 36 into the Concentrator 20 lby means of the sub-atmospheric pressure exerted Within the entire flowpath through the piping of the Concentrator 20, by means of the vacuum producer or pump |85 (preferably of the Water jet type) at the terminal end of the Concentrator. Indeed, it is the suction of this pump that causes the continuall forward progress through the piping of the owpath, by the material being treated therein. Therefore, the vacuum producer or pump |05 has the double purpose of (l) a pump, and `(2) a controller of the pressure within the the iatter will appear hereinafter.

20 (which if desired may be controlled by valve V) through'pipe 36 and inlet 31 at an elevationabove the boiler or vaporizing zone 39 so that such liquor/may fall into the pool or liquid column maintained at a liquid level 8| my means of the barometric leg 48. The barometric leg 40 is so arranged that the range of 'normal fluctuations of the liquid' level 8| is maintained well Ywithin the boiler zone 36in order to assure'efficient vaporization elects on the liquor. Steam is supplied to the encircling jacket 38 to raise the temperature within the boiler zone, to a point in general below the vaporization point of H0104 but above the vaporization point of volatile impurities of its solution. More specifically, the temperature of the zone is such that at the sub-atmospheric pressure existing therein, it is above the dew point of water, since a major purpose of the Concentrator is to evaporate a large amount of water from the HClOi-bearing liquor. In view thereof, the temperature used is such as to insure vaporization of water, even though some HC1O4 may inadvertently also be vaporized. For that reason, it has been found satisfactory to use steam at 50 pounds pressure per square inch to The feeding of the boiler zone 36 from its vapor-exiting end also has proved to be highly ecient. While ordinarily it is not necessary to control the rate of feed of liquor I3 through pipe 36 to the Concentrator, it may be desirable to do so, such for instance if it is desired to minimize the vaporization of the perchloric acid in the vaporizing zone, 33.

So frorr theboiler zone 39, there descends hot liquor of non-volatilized constituents in the liquid column 88 in the barometric leg tu into the of HCl from,

piping. The importance of' 6 :rimase:` A.

pool 4I of the basin42. This liquor tends to remain hot or at least warm enough to discourage sodium salts, such as NaClOt from crystallizing out to any great extent. This liquor,'under nor mal operating conditions of this process and assuming that 'l0-plus percent'of concentrated acid j Vmost of the HCl not previously removed by the Remover and some H0104, which are sucked by the vacuum pump |05 over the curved section 45 into and through the Hot Condenser zone indicated generally by the numeral 44. In Fig. 2, this Hot Condenser zone is shown as having only one condenser unit, but more than one condenser unit may be in the general Hot Condenser zone, so Fig. 3 shows the preferred form wherein two condenser units are used in series. fI'lierefore, the vapors from curved section 45 enter the Hot Condenser unit 8.3 which has an encircling hot water jacket through which water is passed at from 90-95" C., for the purpose of raising the temperature within the condenser unit 83. which in correlation with the sub-atmospheric pressure existing within the tubing in the zone 83, will bring about the condensing of some of the water and some HClOi which may have been carried over. Condensate then flows into the .barometric leg 45 into the column of liquid 01 therein, while vapors which have escaped being condensed pass upwardly through the second Hot Condenser unit are delivered also at atmospheric pressure. It it were not desired to reclaim all possible H0104, the double Hot Condensers neednot beusedfnor the Intermediate Condenser "By their use, a

5 relatively small amount of acid is reclaimed from basins 4l and 01, but usually it is worth this extra effort.

Whereas the function of the Concentrator 2l is to concentrate the H0104 without positive attempt to purify it, the Still 23 has as its function,

treating the concentrated impure acid to purify it. To that end, it vaporizes all the acid, frees such vapor of entrained solids, and then produces a condensate of acid in practically any degree of ,concentration desired, say, from 60% to 73%, al-

though at-the moment the desired grade runs' between '10% and 72% concentration. Another function of the Still is to remove iron-bearing impurities from the acid so that only a few parte per million remain. -The operation of the Still 23 as exemplified in Fig. 3 is-as follows: Concentrated but impure HCl04-bearing liquor from which HC1 and water have been largely removed is s plied to the concentrated liquor pool 5l of 5 basiml 50 whence it is sucked up automatically through liquid column H2 in barometric leg l1 due to the suction existing in the entire 'fiowpath piping or tubing of the Still 2l, as a result oi' vacuum applied thereto by the vacuum producer orpump |43 at the end of the tubing, which has the combined functions of (1) pumping the material through the tubing, (2) applying subfatmospheric pressure thereon, and (3) controlling the degree of pressure (or sub-pressure) within 90 wherein they encounter a second condensing 35 the tubing. The barometric leg is so arranged as Hot Condenser unit 00`als`o descends into the liq` uid column 81 lof the barometric leg 40 and co1- lects in pool 41 of basin 48. Vapors'escaping the second Hot Condensery unit 00 are sucked through'pipe 5| into the Intermediate Condenser 93,'whose jacket 09 is supplied with water at about 20 to 25 C. 'wherein more condensate is yielded which descends into the liquid column 05 of' the barometric leg 94 to Join the pool 90 of basin 91. Vapors escaping uncondensed in this Intermediate Condenser zone are sucked forwardly through pipe 5|' to encounter in the Cold Condenser zone a cold water, spray |04 which does the final condensing, whereupon the condensed uid column |02 maintained in barometric leg 52 and joins pool'53 of basin 54 which passes to waste` ing vapors. This non-gaseous material is then at 2|. From the Cold Condenser zone 50 extends a pipe 40 provided with a pressure indicator |01, a pressure (or vacuum) regulator |00 and the vacuum pump |05. The operator can see from the indicator |01 what pressure is obtaining in the fiowpath piping, and the regulator |06 can be set to regulate automatically the amount of pressure or rather suction, applied to the piping by the pump |05. In this system, satd0 within the boiler zone. The boiler zone is heated to a temperature above that at which, under the pressure existing in the tubing thereof, there is a vaporizing of the volatiles including HCi04 to an extent of about 9.8% of the solution treated .45 in that zone. This is accomplished by supplying steam under, say, 50 pounds pressure per-square inch to the encircling steam jacket of the boiler zone 5I. Liquor within the boiler zone 55 at the temperature. and pressure maintained therein 5 boils so that ebullition takes place and vaporized constituents (comprising on the average HClO `--\60.8%; HCl 0.4%; andHzC 38.8%) of the liquor il! rises. but also there `is splattered up some of the constituents of the liquor along withstheris# Acaught and returned to the boiler zone 54` by some suitable entrapment means. exemplined by the Kjeldahl bulb or head H4. Vapors, comprising all constituents of the liquor Il! volatilizable 00 at the HCl04-vaporizing temperatures obtaining in the boiler zone 56, freed from spray, are sucked forwardly through curved section 0| of the tubing into a Hot Condenser Zone, indicated gener'- ally by -the numeral 6I. A single stage Hot Con-- denser Il, such as is shown in Fig. 2 may be used, Y

but for greater eiiiciency, it is desired to use here a multiple unit Hot Condenser, equipped with two Hot Condenser units in series. So the vapors pass first to Hot Condenser unit I I0 which is iacketed by hot water at between 90 and, say,

95 C., to providea temperature in the tubing of the condenser, which at the pressure existing therein, lies enough below the condensation point of H0104 so that some 80% or 90% thereof con- Remover. All discharges from the Concentrator denses. From this first Hot Condenser unit lll there is conducted through pipe IIB, into the barometric. leg 62 some condensate solution HClOi which descends into the liquid column in the leg 625. Vapors 'which escape condensa-V through the jacket oi the boiler zone causes ebullition of the suspension and vaporization of all of the HC104 present, which rises 'from the boiler zone as vapor.

tion rise in the leg B2 and are sucked through a ,the second Hot Condenser unit |22, that is sim-- liar to the iirst Hot Condenser unit H8, wherein more vapors are condensed which descend into the leg 62 to join'the column of liquid |2U therein. Vapors escaping condensation in unit |22 contain relatively small but significant quantities of HClO4 along with H2O vapor and practically But the ebullition is so violent that ly.

. gravity, into the liquid of the .boiler zone EB, so

all HC1. They are sucked forwardly through pipe 86 into Intermediate Condenser |30, whose jacket is cooled with water at about 20 to 25 C. so that practically all remaining HClO4 and a, quantity of H2O vapors are condensed therein which descend into the liquid column |26 of barometric'leg |25. 'I'his condensate has about 30% acid. Vapors which here escape condensation contain H2O, HCl and traces of HClO4. They are sucked through curved pipe |33 into the Cold Condenser indicated generally by the numeral 65. Whereas the equivalent Cold Condenser in Fig. 2 is shown as being a single unit, for eiciency it is desired to have this a two stage unitinto the iirst unit of whiclr13fi vapors pass from the curved pipe |33. This unit is jacketed and cooled with cold water to a temperature below the dew point of water therein.

Through pipe 5B' is sucked condensate and vapor into the barometric leg tl. descends into the liquid column it@ therein lwhile `vapors rise into the second* Cold Condenser. unit it@ whichis jacketed and 'otherwise like unit i3d. Here the remaining vapors of HC1 and H2O are. condensed and condensate descends into the liquid column |38 of barometriclegilg Thetub- 'ing beyond the Cold Condensers: terminates in a vacuum pump w3 attached -to'fapipe glf associated with which is a pressure indicator bland a pressure regulator |44. The pil-nip is arranged ordinarily to apply 4a degree of vacuumytothe.

i owpath tubing of the Still equal to about 3A inch of mercury; Liquor descending in the Hot Condenser barometric leg 62 into the pool 63 of basin 84 is the iinished product concentrated pure H0104, say, of '11+% concentration. Liquor in the pool 68 of basin 69 goes to waste, while liquor in the pool |21 of basin |28 has enough dilute HC104l to warrant its being redistilled, by being recycled to basin 59, for instance. In the concentrated liquor basin 59,v the concentrated liquor 58 comprises a suspension or slurry of HCiOl and solid impurities such as NaC1O4, which impurities accumulate therein due to theirl descent from the boiler zone 56, and such salts crystallize out. This slurry (Fig. l) may be passed to a second filter station 2t ior separating out the NaClOi for reuse as a starting material, and a nitrate 2l of about 60% acid which can be yreturned to the concentrated liquor 22, to be treated again in the Still. f

The boiler zone 5t oi the Still 23'has such im portant functions, that an enlarged perspective diagrammatic view thereof (with some proportions thereof exaggerated) is-show'n in Fig. 4 .wherein it can be seen that the suspension or slurry from the pool ed of the basin E9 is sucked upwardly through the liquid column M2 in the Condensate through tubing 6l to the subsequent stage-wise v that only vapors pass onward from the bulb H4 condensing zones.

Any solids S' in being rejected from distillation descend literally like a snowstorm, due to Atheir gravity, in the liquid column ||2 of the barometric leg Bluntil they accumulate in the slurry 58 of the basin E9, whereupon periodically the concentrated slurry is supplied to the filter station 2S (Fig. 1) for separation from the acid oi the solids. The solids are recycled to be u as starting material, while the nitrate acid is recycled to the concentrated liquor basin 5u. This treatment of the slurry 58 is not essential. but is desirable for emcient operation so that no acid or NaClOl will be lost. The vertical disposition of the Jacket-,ed boiler zone is important for it is self-cleaning of'itsnon-distillable residue. and in practice it is about 9 feet long. It is self-feeding and maintains its own working level because as liquor is vaporized from the liquid level iii, more liquor is automatically supplied tained substantially constant. However, the level I varies within a limited range due to varying conditions, such as suction, barometric pressure, density of liquor, and so on, although the level is not perfectly constant it is nearly enough so as to maintain a practical working level. i

The non-volatilizable material of the liquor from th'e Concentrator runs normally about 2%. Aside from the NaCl04, the most serious nonvolatilizable contaminating constituent of. the

barometric leg iii until it reaches a liquid level il@ controlled to lie within the boiler zone d@ due to correlating the height of the barometric leg iii and the pressure therein plus the density of the liquid 4suspernsion being treated. Steam passing magma 58 of the basin 59, is-iron. Iron is the most serious because the limit of contamination permittedby the trade is very low, about l part per million.A There is a. tendency of the iron to accumulate in the concentrated liquor 53 because it is very soluble and does not, like NaClOi, crystallize out. Salts of iron gradually cake or bake on the inside of the tubing in the boiler zone adjacent the liquid level H3, but this can be readily removed therefrom periodically during shut-down periods. This method of cleaning also removes some caking at the same point of NaClOl. But this tendency ofthe iron especially to remove itself from lthe liquor andaccumulate in the boiler zone in a manner whereby it can be readily removed, is a highly important advantage flowing from ilus-invention.

As to the worg temperature of the boiler zone 5%, it should meet the requirement oi being high enough to evaporate all of the volatile components of the solution being treated therein, that is the H6104, the water, and the volatile impurities such as HC1. Therefore, the temperature must be correlated with the pressure existing in the boiler zone. At a sub-atmospheric pressure of Hg measured at indicator ldd, preferably used in practicing this process, there is preferably used about 147 C.

vWith respect to the Hot Condenser zone 6@ o the Still 23, a lstudy was made of curves representing the Vapor Pressure of several perchloric acid solutions ranging in concentration from 60% to 73% at temperatures ranging from 130 C.

. down to about 25 C. and of a second set. drawn from values obtained froml the first set'repre'- senting the concentration and. temperature at which perchloric acid solutions will have certain y Vapor Pressures ranging from mm. to 45 mm.

of mercury. From these curves, it was found possible to determine the relations betweenpressure, concentration of acid condensed, and the condensing temperature. For example, ,if vapor is being produced at 20 mm. of Hg (a trifle over %`inch) and condensation is taking place at 106 C. the concentration. should be very close to 71.5%. It', for any reason, the pressure should heat of vaporization, the prevailing conditions must necessarily be favorable to the condensation of strong acid. If this were not the case the acid would have condensed and heated the too cool surface, thus tending to create the favorable conditions. By this means there is maintained at all times a small, but adequate, reservoir of heat (the heat of vaporization of uncondensed `perchioric acid) which tends to keep the inner increase to 25 mm. the acid condensed would be 115 C.no condensation. This clearly indicates the desirability of temperature control.

Bo far, the existence of static equilibrium conditions has been assumed. But under actual working conditions, conditions are no longer staticbut dynamic. Vapor is not stationary but face of the condenser hot enough. Then, by the use of circulating hot water at a controlled temperature, heat is removed at the rate required to keep the condenser cold enough. Thus there is maintained effectively, upper and lower limits. At some intermediate point which is determined by the effects of all the variables', the system adjusts itself and produces condensate which varies in composition between narrow limits, i. e. between 71 and 72% H0104. If it is wished to collect acid containing 'i2-73% HClOi it could be done,A but at the sacrifice of a greater loss of uncondensed acid to the intermediate condenser. The procedure in finding the, proper Hot Condenser temperature is not as diilicult as the explanation of the principles might lead one to believe. The vacuum is controlled at a desired value its" Hg in practice)v and the temperature of the Hot Condenser is set at an arbitrary value.

- If the condensate is weak,`the operator increases movingv rapidly-the velocity is several feet per second. If not condensed within a few seconds in the comparatively short hot condensing zone; the vapor will pass beyond its influence into the intermediate condenser. The rate of distillation between the vapor of the condensing acid and the hot water. Y

The entire Hot Condenser is not surrounded by h'ot water Jackets since this construction would not be very practical. A considerable portion is exposed to air and is therefore air cooled.

Even when insulated the effect of air-cooling is very appreciable, and the roomy temperature varles considerably. It is not practical to maintain pressure and temperature perfectly constant for obvious practical (mechanical) reasons."

This array of forces working against an operator makes the problem seem rather appalling. The fact that the system is dynamic, however. made possible the solution of the problem in a very practical way. Instead of controlling all oi'l the critical factors with the precision which would be required in a static system, there is present another variable 'viz. the amount of HClO4 vapor which is allowed to pass through the-Hot Condenser uncondensed. In other words this condenser is overloaded.

'Ihis new factor overshadows, and to a very large extent eliminates the eifects of the other variables'. It is understandable that, if the vapor leaving the Condenser contains some perchloric acid which would have condensed if it could have found a surface upon which to' dispose-of its INI the temperature until the concentration of the condensed acid in basin 64 is somewhat over 71%. and has an average value 'between 71 and 72.- If the uncondensed acid passing to the subsequent condensers is not excessive, the operator maintains the hot condensers at its present temperature. The operator makes minor adjustments from day to day, on this basis. It is important to remember, however, that temperatures are closely tied to all the factors of pressure, rate of distillation, amount of uncondensed H0104, condensing area, amount of air-cooling, etc.

At 3/4" vacuum (19 to 20 mm.) measured at indicator |45, the Hot Condensers have been operated inthe range 90 C. to 97 C. producing condensate containing 70.95 to 72.05% acid. These are maximum and minimum figures observed by the operators covering a reasonable period. These values may have been exceeded for short periods without .having been observed but the averages are about 93 C. and 71.35% acid.

'I'he length of the various barometric legs are substantially as indicated Aby the scale in feet at the left hand side of Fig. 3. They vary due to the dierence in specific gravity of the liquid in each for maintaining the liquid therein about at the levels shown. Whereas "barometric leg could be interpreted as being a valid description only in case thepressure above the liquid is due to the vapor pressure of the liquid in the barometer" in the practice of this invention, the pressure is regulated by letting in a little air by means of the vacuum regulators!" and ill. Thusthe barometric legs of this invention are almost technically true barometric legs. but` actually they are not' quite so. However, the liquidseal for the leg against breaking the suction, is important. The vertical disposition of the boiler aones is advantageous, but naturally, this and other details of construction shown, can be modified with out departingfrom the spirit of this invention,

'the

chere,

associ creas this invention if b described as treating reaction products of Nacio@ and HCl. it is capable also of similarly t reaction products of Ba (C104) s and =l l.

claim:

1. The process of making perchloric acid which comprises reacting hydrochloric acid with a perchlorate of a metal of the group consisting oi sodiumand barium under such conditions that a solid chloride and a solution cf perchlcric acid with said chloride are obtained, septhe solid chloride, and removing unreacted acid from the solution. dis- ;.f the solution under sub-atmospheric pres- 'ff l w' which form in the s acne t a' isometric column esdowar from the lcottom of the dis- .la met, md -Tr orio d vapors from y E. x'l d f if at sub-atmospheric t ta-in a pool at atmospheric a quantity of concentrated acid su a ometric col mr .1 oi' such acid c zone, settling suspended components residual in that zone 'through w liquid G91 1"- "t t0 th@ l fOr 'il .l It 'A1 Ill the t lportion of the coliro ai thereof open to the atmosthat pool a solution ci such .1 avapo sono to a least to that at which such l the solution in the pressure und through as column ma n on thereof, automati conat a temerature correlated to said I g Zell, .v =-1 the elevation of the li uid rf from thenorimng zone into a controlling the liquid level of the column to mainlt at substantially constant elevation. continually settling such crystals from the vaporizing section substantially as fast they ic therein downwardly through the liquid co1 to its pool simultaneously with the up-ieed ot acid in the same col, removinssettied solids from the pool, sucking vaporized material from the vaporizing section into a condensing zone maintained at sub-atmospheric pressure, and collectins condensate from the condos zone condensed from the vaporized material ente auf' the condensing sono. Y

e. The pro according to claim 3 wherein non-vaporized material spraying upwardly iront the vapo s, y.s sone is caught from further nait and returned through said the lthereo.

5 The process accordinsr to cm 3 withv the additional steps of filtering liquid suspeon taken from the pool of the vaporizing zone to wt its solid and liquid constituents, and returning ltrate to the process. v

6. The process ci purifying impure perchloric acid containing dissolved crystallizable solid im= he treated in solution into a vaporizing lzone maintained under sub-atmospheric pressure wherein non-perchloric acid constituents crystallize as solids; maintaining terminating in that zone a column of liquid supported from a pool thereof open to the atmosphere and derived from such material; maintaining the solution in the Vvapc'a'rizins zone heated to a temperature equal to that at which such acid distills and crystals l form thereinwhile 'u A uv circulationin that sone, continually settling such crystals from the vaporizing zone through its liquid column to its pool substantially asA fast as 'they present thermselvesrin thevaporizing zone, removing settled crystals from that pool, sucking vaporized matelrial from the vapo 1.

y sure, collecting condensate therefrom in a column oi' auch conde supported from a pool'thereci. su v 4:a vanorized material from the condens- 50 ing'zone into a further condensing zone at subatmospheric pressure and cooled to a temperature below water's dew-point as it exists within said further zone; and removing liquid material from each oi said pools whereby dierent con- 55 centrations of acid are obtained with the nrst- -r f therein. sucking feed acid"` mentioned pool ci' condensate furnishing the strongest acid.

' 'JOHN C. T. 

